The invention relates to analyzing gaseous and solid materials, particularly components containing oxygen, and more particularly to an oxygen analyzer capable of identifying and classifying microgram quantities of oxygen in ambient particulate matter.
Numerous methods and apparatus have been developed for the analysis of matter, particularly by different types of pyrolysis ovens utilizing various types of sample holding structures and product evaluation techniques. These prior known approaches are exemplified by U.S. Pat. No. 1,515,237 issued Nov. 11, 1924 to T. D. Yensen; U.S. Pat. No. 3,252,759 issued May 24, 1966 to W. Simon; U.S. Pat. No. 3,374,064 issued Mar. 19, 1968 to O. L. Kolsto; U.S. Pat. No. 3,861,874 issued Jan. 21, 1975 to A. E. Krc; and U.S. Pat. No. 4,244,917 issued Jan. 13, 1981 to R. A. Woods et al.
More recently there has been an increased interest in determining the content of ambient particulate matter. The particulate matter is collected by filter sampling methods well known in the art and then analyzed to determine the components in the particulate matter, as well as a quantitative assessment of the components.
Ambient aerosol particles, complex mixtures of organic and inorganic chemical compounds, can yield information on the aerosol origins and atmospheric transformations when speciated. The major anthropogenic species are compounds of carbon, hydrogen, oxygen, nitrogen, and sulfur. Of these compounds, oxygen has traditionally been the most difficult to analyze, requiring a complex procedure or special apparatus to perform the analysis. There are currently two known and established aerosol compound speciation procedures, either of which may be used in analyzing devices.
The most common of these two processes involves a system in which a weighed sample is placed in a quartz pyrolysis tube containing platinized carbon. Oxygen in the gaseous combustion products are converted to carbon monoxide by passage through the platinized carbon and the carbon monoxide is subsequently oxidized to carbon dioxide by passage over copper oxide. The sample is pyrolyzed in a helium atmosphere so that carbon monoxide is formed from oxygen in the sample and so that the platinized carbon does not burn. The carbon monoxide is oxidized by the copper oxide to form carbon dioxide, which is detected and measured, giving the total oxygen concentration in the sample. This procedure or process may, for example, be carried out in a Perkin-Elmer Model 240 Elemental Analyzer made by Perkin-Elmer Corp., Norwalk, Conn., which incorporates features of above-referenced U.S. Pat. No. 3,252,759.
The other of these procedures or processes uses the normal inert gas-fusion method as a basis for determining oxygen released at successively higher temperatures. The sample is heated in a graphite crucible, current is increased in discrete steps using a program tailored for the specific oxides believed to be present. The oxygen peaks are plotted against temperature on an integral printer, yielding information about individual compounds present in the sample. This process may, for example, be carried out in a LECO RO-16 Oxygen Determinator, made by LECO Corp., St. Joseph, Mich.
While the above-referenced processes and apparatus have been effective, they have been found to lack the necessary sensitivity for certain types of analysis. Thus, a need exists for an oxygen analysis procedure and apparatus which provides greater sensitivity than the currently known approaches.